SCH vs AST?

[winsock]

I hate to be that guy but there are multi pages threads right below you discussion this topic. The bottom line is AST isn't as reliable as the other two are because of less emergency heals and oh-shit that is happening buttons. But really to get a full understanding please read those threads.

Lol don't worry about being that guy. If it not "use search" its "don't necro" or "don't derail"

Question though, how does it have less 'oh-shit' stuff than SCH?
AB is instant on gcd
ED is instant
Benefic II is a proc for instant
Light speed causes several things to be instant

I guess where im coming from is AST definitely doesnt throw out WHM heals, but SCH doesnt either and is still considered good. SCH has lustrate saves, but AST has access to more AoE than SCH and its saves are more accessible